This invention relates to shredding machines and more particularly to a machine capable of accommodating lightweight feed materials.
One type of machine commonly used to shred practically any type of refuse, from metal scrap to waste paper, employs a rapidly revolving rotor which carries swing hammers past a grate. Actually, the grate is mounted at the bottom of a housing in which the rotor revolves, and this housing has at its top a large opening through which the refuse is introduced into the machine. The refuse falls into the circular path described by the hammers, and the hammers carry the refuse across the grate where it is shredded. The shredded refuse drops through the openings in the grate to fall out of the machine in a highly condensed form.
Machines of the foregoing character function quite well with heavy or dense refuse such as metal and most wood scrap. However, lightweight refuse,such as loose newspaper and corrugated paperboard, tends to be air-supported or bouyed, or at least cannot be fed evenly into the machine.
The problem resides in the windage developed by the rotor within the confines of the housing. In this regard, the machine acts like a giant fan, drawing air into the housing along one side of the inlet and through the grate and discharging it with considerable velocity through the inlet. Light materials, such as corrugated paperboard, tend to remain suspended in this airstream and indeed accumulate in the airstream above the rotor until the weight of the accumulated materials is enough to overcome the suspension effect, at which time the entire mass of accumulated material drops downwardly into the revolving hammers on the rotor. This overloads the rotor, causing it to bog down and perhaps stall. Thus, the windage created by a conventional shredding machine prevents the machine from accepting lightweight feed materials uniformly, so when used to reduce such materials, the machine does not operate evenly, but instead in surges. This in turn places undue stress on the machine, consumes more energy, and results in less efficient operation.
The foregoing problem could perhaps be eliminated by reducing the size of the inlet and locating it entirely to that side of the rotor at which the hammers pass over top center and descend. This, however, reduces the capacity of the machine and as a result the machine will not accept large items of refuse.